This invention relates to dispersant-viscosity improvers for lubricating oils, oil compositions and concentrates containing such dispersant-viscosity improvers, and a process for preparing such dispersant-viscosity improvers.
The viscosity of oils of lubricating viscosity is generally dependent upon temperature. As the temperature of the oil is increased, the viscosity usually decreases, and as the temperature is reduced, the viscosity usually increases.
The function of a viscosity improver is to reduce the extent of the decrease in viscosity as the temperature is raised or to reduce the extent of the increase in viscosity as the temperature is lowered, or both. Thus, a viscosity improver ameliorates the change of viscosity of an oil containing it with changes in temperature. The fluidity characteristics of the oil are improved.
Viscosity improvers are usually polymeric materials and are often referred to as viscosity index improvers.
Ester group containing polymers are well-known additives for improving the fluidity characteristic of lubricating oils. Polyacrylate, particularly polymethacrylate ester polymers are well-known and are widely used for this purpose.
Dispersants are also well-known in the lubricating art. Dispersants are employed in lubricants to keep impurities, particularly those formed during operation of machinery, in suspension rather than allowing them to deposit on the surfaces of lubricated parts.
Multifunctional additives that provide both viscosity improving properties and dispersant properties are likewise known in the art. Such products are described in numerous publications including Dieter Klamann, xe2x80x9cLubricants and Related Productsxe2x80x9d, Verlag Chemie Gmbh (1984), pp. 185-193; C. V. Smalheer and R. K. Smith xe2x80x9cLubricant Additivesxe2x80x9d, Lezius-Hiles Co. (1967); M. W. Ranney, xe2x80x9cLubricant Additivesxe2x80x9d, Noyes Data Corp. (1973), pp. 92-145, M. W. Ranney, xe2x80x9cLubricant Additives, Recent Developmentsxe2x80x9d, Noyes Data Corp. (1978), pp. 139-164; and M. W. Ranney, xe2x80x9cSynthetic Oils and Additives for Lubricantsxe2x80x9d, Noyes Data Corp. (1980), pp. 96-166. Each of these publications is hereby expressly incorporated herein by reference.
Derivatives of polyacrylate esters are well-known as additives for lubricants that provide not only improved viscosity characteristics, but also may enhance dispersant properties of lubricants.
It is desirable that the viscosity improver or dispersant viscosity improver not adversely affect the low-temperature viscosity of the lubricant containing same. Frequently, while viscosity improvers or dispersant viscosity improvers enhance the high temperature viscosity characteristics of lubricating oil, that is, they reduce the loss of viscosity with increasing temperature, low temperature properties of the treated lubricant become worse.
One of the major requirements for automatic transmission fluids has been improved low temperature performance. This is demonstrated by requirements for maximum Brookfield viscosities of 50,000, 20,000, or even 10,000 centipoise at xe2x88x9240xc2x0 C. The viscosity modifier, which can comprise nearly 50 weight percent and sometimes even more of the total additive system employed in an automatic transmission fluid can have a major impact on the low temperature performance. Such characteristics are also desirable in other applications such as in gear lubricants and manual transmission fluids. The copolymers of this invention are also useful in many other lubricating oil compositions including, but not limited to engine oils, hydraulic oils, industrial oils, etc.
Accordingly, it is desirable to provide compositions that reduce the extent of loss of viscosity at high temperatures while not adversely increasing the low temperature viscosity of lubricating oil compositions.
It is a primary object of this invention to provide novel multi-purpose lubricant additives.
A more specific object is to provide multi-purpose additives directed to improving the viscosity and dispersant properties of a lubricating composition.
A further object is to provide processes for preparing such multi-purpose additives.
Still another object is to provide additive concentrates containing the novel multi-purpose lubricant additives of this invention.
Yet another object is to provide lubricants having improved dispersant and viscosity properties.
Other objects will in part be obvious in view of this disclosure and will in part appear hereinafter.
The present invention is directed to a process for preparing a nitrogen containing copolymer comprising reacting, in the presence of a free radical initiator,
(A) from about 55% to about 99.9% by weight of one or more alkyl acrylate ester monomers containing from 1 to about 24 carbon atoms in the ester alkyl group, wherein at least about 50 mole % of the esters contain at least 6 carbon atoms in the ester alkyl group, and
(B) from about 0.1% to about 45% by weight of at least one nitrogen containing monomer selected from the group consisting of vinyl substituted nitrogen heterocyclic monomers, dialkylaminoalkyl acrylate monomers, dialkylaminoalkyl acrylamide monomers, N-tertiary alkyl acrylamides, and vinyl substituted amines provided that the total of (A) and (B) equals 100%, and optionally, in the presence of a chain transfer agent,
wherein monomer (A), the free radical initiator, and if used, the chain transfer agent, are first combined to form a mixture, whereupon from about 10% to about 80% of said mixture is mixed with monomer (B);
from about 20% to about 100% of the mixture of monomers (A) and (B) is heated until an exotherm is noted, then while maintaining reaction temperature, first adding the balance, if any, of the mixture of monomers (A) and (B), over about 0.25 hour to about 5 hours followed by addition over 0.25 to about 5 hours of the remaining mixture of monomer (A) and initiator, optionally adding additional initiator, whereupon the reaction is continued to completion.
This invention also relates to a polyacrylate ester, and more particularly a polymethacrylate ester based dispersant-viscosity improver for lubricating oil compositions. Specifically, the dispersant viscosity improvers of this invention are nitrogen-containing copolymers.
The present invention also relates to additive concentrates and lubricating oil compositions containing compositions prepared by the process of this invention.
As used herein, the terms xe2x80x9cacrylatexe2x80x9d and xe2x80x9cacrylamidexe2x80x9d include the 2-alkyl acrylates and 2-alkyl acrylamides, particularly C1-4 alkyl-, and especially, methacrylates and methacrylamides.
The present invention provides a process for preparing a composition of matter suitable for use as a dispersant-viscosity improver for lubricating oil compositions comprising nitrogen-containing copolymers derived from one or more alkyl acrylate ester monomers containing, from 1 to about 24 carbon atoms in the ester alkyl group and at least one nitrogen-containing monomer as described in greater detail hereinbelow.
As used herein, the terms xe2x80x9chydrocarbonxe2x80x9d, xe2x80x9chydrocarbylxe2x80x9d or xe2x80x9chydrocarbon basedxe2x80x9d mean that the group being described has predominantly hydrocarbon character within the context of this invention. These include groups that are purely hydrocarbon in nature, that is, they contain only carbon and hydrogen. They may also include groups containing substituents or atoms which do not alter the predominantly hydrocarbon character of the group. Such substituents may include halo-, alkoxy-, nitro-, etc. These groups also may contain hetero atoms. Suitable hetero atoms will be apparent to those skilled in the art and include, for example, sulfur, nitrogen and oxygen. Therefore, while remaining predominantly hydrocarbon in character within the context of this invention, these groups may contain atoms other than carbon present in a chain or ring otherwise composed of carbon atoms.
In general, no more than about three non-hydrocarbon substituents or hetero atoms, and preferably no more than one, will be present for every 10 carbon atoms in the hydrocarbon or hydrocarbon based groups. Most preferably, the groups are purely hydrocarbon in nature, that is they are essentially free of atoms other than carbon and hydrogen.
Throughout the specification and claims the expression oil soluble or dispersible is used. By oil soluble or dispersible is meant that an amount needed to provide the desired level of activity or performance can be incorporated by being dissolved, dispersed or suspended in an oil of lubricating viscosity. Usually, this means that at least about 0.001% by weight of the material can be incorporated in a lubricating oil composition. For a further discussion of the terms oil soluble and dispersible, particularly xe2x80x9cstably dispersiblexe2x80x9d, see U.S. Pat. No. 4,320,019 which is expressly incorporated herein by reference for relevant teachings in this regard.
It must be noted that as used in this specification and appended claims, the singular forms also include the plural unless the context clearly dictates otherwise. Thus the singular forms xe2x80x9caxe2x80x9d, xe2x80x9canxe2x80x9d, and xe2x80x9cthexe2x80x9d include the plural; for example xe2x80x9ca monomerxe2x80x9d includes mixtures of monomers of the same type. As another example the singular form xe2x80x9cmonomerxe2x80x9d is intended to include both singular and plural unless the context clearly indicates otherwise.
In the context of this invention the term xe2x80x9ccopolymerxe2x80x9d means a polymer derived from two or more different monomers. Thus, a polymer derived from a mixture of, for example, methyl-, butyl-, C9-11-, and C12-18- acrylates is a copolymer as defined herein. The copolymers of this invention also contain units derived from nitrogen-containing monomers.
The nitrogen-containing copolymers of this invention may be prepared by a process comprising reacting, in the presence of a free radical initiator,
(A) from about 55% to about 99.9% by weight, preferably from about 75-99.5% by weight, more preferably from about 90 to about 99%, often from about 80 to about 99% by weight of one or more alkyl acrylate ester monomers containing from 1 to about 24 carbon atoms in the ester alkyl group, wherein at least about 50 mole % of the esters contain at least 6 carbon atoms, preferably at least 8 carbon atoms, in the ester alkyl group, and
(B) from about 0.1% to about 45% by weight, preferably from about 0.5 to about 25% by weight, often from about 0.5 to about 20%, often from about 1% to about 20%. more preferably from about 1 to about 10% by weight of at least one nitrogen containing monomer selected from the group consisting of vinyl substituted nitrogen heterocyclic monomers, dialkylaminoalkyl acrylate monomers, dialkylaminoalkyl acrylamide monomers, N-tertiary alkyl acrylamides, and vinyl substituted amines, provided that the total of the percentages of (A) and (B) equals 100%, and optionally, in the presence of a chain transfer agent,
wherein monomer (A), the free radical initiator, and if used, the chain transfer agent, are first combined to form a mixture, whereupon from about 10% to about 80% of said mixture is mixed with monomer (B), heating from about 20% to 100%, often from about 20% to about 80%, more often from about 30% to about 60%, and in one preferred embodiment 100%, of said mixture until an exotherm is noted, then while maintaining reaction temperature, first adding the balance, if any, of the mixture of monomers (A) and (B) over about 0.25 hour to about 5 hours followed by addition over 0.25 to about 5 hours of the remaining mixture of monomer (A) and initiator, then optionally adding additional initiator, whereupon the reaction is continued to completion.
Any combination of the foregoing ratios of reactants is useful provided the total percentages equals 100%.
While addition of additional initiator after all of the monomers are in the reaction is optional, it is often beneficial to utilize one or more additional amounts of initiator to facilitate driving the reaction to completion. As noted, one or more increments, usually one or two increments of additional initiator is used, usually followed by a period of heating at reaction temperature for about 0.25 to about 3 hours after each increment. The skilled person will readily recognize the need for additional initiator at this stage of the process by determining the extent of reaction, for example by infrared analysis to determine the presence of unreacted monomer or by other techniques such as measuring the viscosity of the reaction product.
The nitrogen-containing copolymers of this invention are frequently prepared in an organic diluent. It has been determined that specific amounts and types of diluent present in the nitrogen-containing copolymers of the invention can have a pronounced effect on the low temperature viscosity properties of lubricants containing them.
(A) The Alkyl Acrylate Ester Monomer
As stated hereinabove, the nitrogen-containing copolymer comprises units derived from (A) alkyl acrylate ester monomers containing from 1 to about 24 carbon atoms in the ester alkyl group, wherein at least about 50 mole % contain at least 6, preferably at least 8, carbon atoms in the ester alkyl group. More often (A) comprises a mixture of ester monomers, having from about 5% to about 75% by weight, preferably from about 30% to about 60% by weight of alkyl acrylate ester monomers containing from 1 to 11 carbon atoms in the ester alkyl group and (B) from about 25% to about 95% by weight, preferably from about 40% to about 70% by weight of alkyl acrylate ester monomers containing from 12 to about 24 carbon atoms in the ester alkyl group, wherein as noted hereinabove, at least about 50 mole % contain at least 6 carbon atoms, preferably at least 8 carbon atoms, in the ester alkyl group. In an especially preferred embodiment, the alkyl acrylate ester monomers comprise alkyl methacrylate esters.
In one particular embodiment, monomer (A) comprises at least 5% by weight of alkyl acrylate esters having from 4 to 11 carbon atoms in the ester alkyl group. In another embodiment, monomer (A) comprises from about 5% to about 40%, often from about 10% to about 40% by weight alkyl acrylate esters having from 1 to 4 carbon atoms in the ester alkyl group. In still another embodiment, monomer (A) comprises from about 60% to about 90% by weight of alkyl acrylate esters having from 9 to 11 carbon atoms in the ester alkyl group.
In one preferred embodiment, monomer (A) consists essentially of C12-24, often C12-18, and frequently C12-15 methacrylates.
The acrylate ester monomers can be prepared by conventional methods well known to those of skill in the art. For example, acrylate ester monomers are most often prepared via the propylene oxidation process, a two stage vapor phase oxidation of propylene to acrylic acid, which is then esterified to the desired ester. Previously, the manufacture of acrylates involved the petrochemistry of materials such as acetylene, acrylonitrile and others.
For methacrylates, processes used often vary, depending on the desired monomer. The acetone cyanohydrin process involves the reaction of acetone with HCN to form acetone cyanohydrin which is then reacted with the desired alcohol to form the ester. Propylene carbonylation and many other processes are also used.
A variety of procedures are described in considerable detail in the section entitled xe2x80x9cAcrylic and Methacrylic Ester Polymersxe2x80x9d in the Encyclopedia of Polymer Science and Engineering, Vol. 1, pp. 247-251, Wiley-Interscience, New York (1985).
Many alkyl acrylate esters are commercially available. Suppliers include, RohMax; San Esters Corp., with offices in New York, N.Y.; Mitsubishi Rayon Co. Ltd.; Polysciences, Inc., Warrington, Pa.; Sartomer Co., Exton, Pa.; and others.
(B) The Nitrogen-Containing Monomer
The nitrogen-containing copolymers of this invention also comprise units derived from (B) from about 0.1% to about 45% by weight, often up to about 20% by weight, and in one embodiment from about 0.5% to about 10% by weight, especially from about 1.5% to about 8% by weight of at least one nitrogen-containing monomer selected from the group consisting of vinyl substituted nitrogen heterocyclic monomers, dialkylaminoalkyl acrylate monomers, dialkylaminoalkyl acrylamide monomers, N-tertiary alkyl acrylamides, and vinyl substituted amines.
In one embodiment, the nitrogen-containing monomer is an N-vinyl substituted heterocyclic monomer. Examples of such monomers include N-vinyl imidazole, N-vinyl pyrrolidinone and N-vinyl caprolactam.
In another embodiment, the vinyl substituted heterocyclic monomer is vinyl pyridine.
In yet another embodiment, the nitrogen-containing monomer is a N,N-dialkylaminoalkyl acrylamide or acrylate wherein each alkyl or aminoalkyl group contains, independently, from 1 to about 8 carbon atoms.
In a further embodiment, the nitrogen-containing monomer is a tertiary-alkyl acrylamide, preferably tertiary butyl acrylamide.
The Diluent
As noted hereinabove, the copolymers of this invention may be prepared in the presence of a diluent. A diluent may also be added to a substantially diluent-free copolymer, usually by dissolving or dispersing the substantially diluent-free polymer in an appropriate diluent. In another embodiment, an additional diluent, often a higher boiling diluent such as an oil, may be added to a copolymer which was prepared in, and still contains, a lower boiling diluent which is then removed by common methods such as distillation.
In one embodiment, the diluent is a mineral oil. In a preferred embodiment the mineral oil consists essentially of hydrotreated naphthenic oil. Also contemplated are hydrodewaxed mineral oils.
The diluent may also be a synthetic oil. Common synthetic oils are ester type oils, polyolefin oligomers or alkylated benzenes.
The diluent-containing copolymers of this invention are referred to herein as additive concentrates. Such additive concentrates are then added, along with other desirable performance-improving additives, to an oil of lubricating viscosity to prepare the finished lubricant composition.
The additive concentrates preferably comprise from about 25% to about 90% by weight of copolymer, preferably from 35% to about 85% by weight, and from about 10% to about 75% by weight of diluent, preferably from about 15% to about 65% by weight of diluent.
As is often the case in the art, performance improving additives may be combined with the polymers of this invention, together with a diluent as defined herein, to form a single additive concentrate which can then be mixed with an oil of lubricating viscosity to form a lubricating oil composition.
In one embodiment, selection of diluents having particular characteristics leads to enhanced performance of dispersant-viscosity improvers of this invention. For example, lubricating oil compositions comprising additive concentrates containing certain diluents together with the nitrogen-containing polymers of this invention have enhanced low temperature characteristics. Particularly valuable are lubricating oil compositions that display excellent viscosity characteristics at very low temperatures, for example, from xe2x88x925xc2x0 C. to xe2x88x9240xc2x0 C.
The certain diluents that impart surprising and exceptional low temperature performance when used in conjunction with the dispersant viscosity improvers of this invention, have in common very low viscosity at very low temperatures. In particular they all display Brookfield viscosities (expressed in centipoise) at xe2x88x9226xc2x0 C. ranging from about 50 to about 400, more preferably from about 80 to about 200. At xe2x88x9240xc2x0 C. useful oils have Brookfield viscosities (expressed in centipoise) ranging from about 100 to about 1500, more preferably from about 125 to about 600. Brookfield viscosities are determined employing ASTM Procedure D-2983 described in greater detail hereinafter. These particularly useful diluents display viscosities (ASTM Procedure D-445) at 40xc2x0 C. ranging from about 2.5 to about 6 centistokes and at 100xc2x0 C. ranging from about 1 to about 2.5 centistokes.
Included among such useful diluents are naphthenic oils, hydrotreated naphthenic oils, and alkylated aromatics, particularly alkylated benzenes having at least one alkyl group containing from about 8 to about 24 carbon atoms, preferably from about 12 to about 18 carbon atoms. Especially useful are hydrotreated naphthenic oils, examples being Risella G-07 from Shell Oil, Cross Oil Co.""s L-40, a 40 neutral hydrotreated naphthenic oil and L-60, which is a 60 neutral oil.
Low temperature viscosity (Brookfield Viscosity) of fluid lubricants is determined using ASTM Procedure 2983, Standard Test Method for Low Temperature Viscosity of Automotive Fluid Lubricants Measured by Brookfield Viscometer, which appears in the Annual Book of ASTM Standards, Section 5, ASTM, Philadelphia, Pa., USA. This procedure employs a Brookfield Viscometer which is described in the procedure. The device is available from Brookfield Engineering Laboratories, Stoughton, Mass., USA.
ASTM Procedure D-445 is described hereinafter.
Chain Transfer Agents
The process may be conducted in the presence of a chain transfer agent. The use of chain transfer agents to regulate and limit molecular weight in polymer reactions is known, see for example xe2x80x9cConcise Encyclopedia of Polymer Science and Engineeringxe2x80x9d, J. I. Kroschwitz, Ed., Wiley-Interscience (New York, 1990), page 139.
An extensive discussion of chain transfer, its effects, and chain-transfer agents together with an extensive bibliography, appears in the xe2x80x9cEncyclopedia of Polymer Science and Technologyxe2x80x9d, H. F. Mark, N. G. Gaylord, and N. M. Bikales, Eds., Interscience, (New York, 1965), pp. 575-610. Both of these are expressly incorporated herein by reference.
For the present application, sulfur compounds, especially mercaptans, particularly tertiary dodecyl mercaptan, are preferred.
The Nitrogen-Containing Copolymer
The products obtained by the process of this invention are copolymers of this invention have a weight average molecular weight (Mw) ranging from about 10,000 to about 500,000, more often from about 30,000 to about 250,000, frequently from about 20,000 to about 100,000 and polydispersity values (Mw,/Mn) ranging from about 1.2 to about 5.
Molecular weights of polymers are determined using well-known methods described in the literature. Examples of procedures for determining molecular weights are gel permeation chromatography (also known as size-exclusion chromatography) and vapor phase osmometry. These and other procedures are described in numerous publication including:
P. J. Flory, xe2x80x9cPrinciples of Polymer Chemistryxe2x80x9d Cornell University Press (1953), Chapter VII, pp. 266-316, and
xe2x80x9cMacromolecules, an Introduction to Polymer Sciencexe2x80x9d, F. A. Bovey and F. H. Winslow, Editors, Academic Press (1979), pp. 296-312.
W. W. Yau, J. J. Kirkland and D. D. Bly, xe2x80x9cModem Size Exclusion Liquid Chromatographyxe2x80x9d, John Wiley and Sons, New York, 1979.
A measurement which is complementary to a polymer""s molecular weight is the melt index (ASTM D-1238). Polymers of high melt index generally have low molecular weight, and vice versa. Mooney Viscosity (ASTM Procedure D-1646-87) relates indirectly to polymer molecular weight. All other factors being equal, as molecular weight of the polymer increases, so too does the Mooney viscosity.
ASTM Procedures D-1238 and D-1646-87 appear in Volumes 8 and 9, respectively, of the aforementioned Annual Book of ASTM Standards.
A preferred method, and the method employed to determine the molecular weights of polymers as set forth herein, is gel permeation chromatography (GPC) employing polyacrylate standards.
As noted hereinabove, acrylic copolymers have been previously prepared by several different techniques. In one embodiment, the acrylate ester monomers and nitrogen-containing monomer are reacted together. In another embodiment, the acrylate esters are reacted to form an acrylate ester copolymer backbone onto which is grafted a nitrogen-containing monomer. In still another embodiment, a mixture of acrylate and nitrogen-containing monomers may be grafted onto a preformed acrylate ester polymer backbone.
In the first embodiment, a mixture of monomers is charged to a reactor together with, if desired, diluent and again, if desired, chain transfer agent. The materials are stirred under a nitrogen atmosphere. Subsequently, a polymerization initiator is added and the materials are heated to reaction temperature. The reaction is continued until the desired degree of polymerization is attained.
In the second embodiment, the acrylate monomers are polymerized, then the grafting of the nitrogen-containing monomer onto the preformed acrylate ester copolymer is accomplished. A mixture of additional acrylate monomers together with nitrogen-containing monomer may be grafted onto the preformed acrylate ester polymer.
In the grafting process, additional initiator is usually employed during the grafting step. In either process, additional initiator may be added during processing.
In another previously used method, the monomers are polymerized incrementally. A mixture of monomers together with a polymerization initiator is prepared. A portion, typically about 20% to about 40%, more often about 33%, of the mixture, is charged to a reactor with the balance being placed in an addition vessel. The reactants are heated under a nitrogen atmosphere until an exothermic reaction is noted. When the exothermic reaction begins to subside, addition of the balance of the monomer-initiator mixture is begun, while maintaining, via heating or cooling, as needed, the desired reaction temperature.
The process of this invention relates to a new procedure. In this process, monomer (A), the free radical initiator and if used, the chain transfer agent are first combined to form a mixture, whereupon from about 10% to about 80% of said first mixture is mixed with monomer (B). From about 20% to about 100% of this mixture is then heated until an exotherm is noted. Thereafter, while maintaining reaction temperature, the balance, if any, of the remaining mixture of monomers (A) and (B) is added followed by the addition of the remaining monomer (A) and initiator and if used, chain transfer agent, then optionally, adding one or more increments of additional initiator and continuing the reaction to completion.
Frequently, when nitrogen-containing copolymers are prepared, the preparation has an odor which is often considered to be objectionable. While not wishing to be bound by theory, it is considered unlikely that the polymer, per se, possesses any noticeable odor. One theory is that the odor may arise from the presence of small amounts of unreacted monomer, particularly nitrogen-containing monomer, or small amounts of other impurities. The copolymers prepared by the process of this invention have been found to be substantially free of objectionable odor.
Polymerization can take place under a variety of conditions, among which are bulk polymerization, solution polymerization, emulsion polymerization, suspension polymerization and nonaqueous dispersion techniques.
The process of this invention makes use of the conventional methods of radical copolymerization.
Such methods are described in the work xe2x80x9cEncyclopedia of Polymer Science and Engineeringxe2x80x9d (H. F. Mark, N. M. Bikales, C. G. Overberger and G. Menges), 2nd edition (1988), published by Wiley Interscience.
These methods include free-radical initiated polymerization employing azo compounds or peroxides. Also described therein are photochemical and radiation initiated methods.
Useful initiators include organic peroxides, hydroperoxides and azo compounds. Redox initiators are also useful.
Molecular weights of the polymers can be controlled employing a number of techniques including choice of initiator, reaction temperature, concentration of monomers and solvent type. As noted previously, chain transfer agents can be used.
Free radical generating reagents useful as polymerization initiators are well known to those skilled in the art. Numerous examples of free radical initiators are mentioned in the above-referenced texts by Flory and Bovey and Winslow. An extensive listing of free radical initiators appears in J. Brandup and E. H. Immergut, Editors, xe2x80x9cPolymer Handbookxe2x80x9d, 2nd edition, John Wiley and Sons, New York (1975), pp. II-1 to II-40. Numerous free radical initiators are available and many are commercially available in large quantities. Included among free radical initiators are t-butyl peroxide, t-butyl hydroperoxide, t-amyl peroxide, cumyl peroxide, dibenzoyl peroxide (Aldrich), t-butyl m-chloroperbenzoate, azobisvaleronitrile, t-butyl peroctoate and tertiary-butyl perbenzoate, (Trigonox 21 and Trigonox C, respectively, both from AKZO) and 2,2xe2x80x2-azobis(isobutyronitrile), VAZO-64, and, 2,2xe2x80x2-azobis(methylbutyronitrile), VAZO-67, both from DuPont.
Free radical initiators are usually used in amounts ranging from about 0.01% to about 10 percent by weight based on the total weight of reaction mixture. Generally, the initiators are used at about 0.05% to about 3% by weight, even more often from about 0.1 to about 1% by weight.
The choice of free radical initiator can be an important consideration. Considerations include the half-life of the initiator at a given temperature, nature of the reactants, reaction temperature, solvent or diluent, and the like.
The products of the present invention are generally prepared at reaction temperatures ranging from about 60xc2x0 C. to about 160xc2x0 C. The half-life of an initiator at a given temperature is an important consideration.
Because acrylic polymerizations are usually accompanied by liberation of considerable heat, care must be taken to avoid uncontrolled reaction. Temperatures can be controlled by using reactors with cooling jackets, controlling rates of addition and use of reaction solvents.
While the process of the instant invention is conducted in conventional reactors employing agitation means including mechanical stirrers or circulating pumps, another useful means for preparing the copolymers of this invention is to employ a high energy mechanical mixing device. These include roll mills, ball mills or extruders. Of these, extruders are preferred since the comonomers can be fed to the feed hopper in any desired fashion. Methods of employing such devices, and especially extruders, are described in a number of patents including Hayashi et al, U.S. Pat. No. 4,670,173 and Sopko et al, U.S. Pat. No. 5,039,433, both of which are expressly incorporated herein by reference.
The following examples are intended to illustrate several compositions of this invention as well as means for preparing same. Unless indicated otherwise all parts are parts by weight. It is to be understood that these examples are intended to illustrate several compositions and procedures of the invention and are not intended to limit the scope of the invention. Molecular weight values are determined employing gel permeation chromatography (GPC) employing well-characterized polymethacrylate (PMA) calibration standards. Filtrations are conducted using a diatomaceous earth filter aid.